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Understanding the Big Picture

Matthew Holm

September 1, 1995

Understanding the Big Picture

Aside from the occasional impromptu napkin scribble, the last time I had to draw a map was in second grade, when Mrs. Heimer gave us brightly colored workbooks that showed just how it was done. One hour, three afternoons a week, we drew the various symbols guaranteed to be useful for life: tiny trees for forests, wavelets covering splotches of blue for lakes or seas, and my favorite, the bridge. It looked something like two reversed brackets ][ but Mrs. Heimer promised it was universally read as "bridge."

I've never needed to draw a bridge since, and I've never once seen waves gracing the lakes and seas of Rand McNally. Professional cartographers would seem to have their own set of rules.

But as Cindy Brewer of Penn State's geography department tells me, map makers don't necessarily understand how people read maps, and often draw them in confusing ways. Her work has been to make maps easy to read and easy to draw. "I'm trying to be real systematic," she says. "What do you do with color to have the map make sense?"

Brewer works not with road atlases, but with thematic maps of death rates, employment rates, or weather data, for example. Color choice in this type of map is very important, because the relationships between the colors determine how easily data trends can be seen.

Brewer understands color: her undergraduate work at the University of Guelph was not in geography, but art. The art training made her familiar with color theory, and later, for her master's thesis at Michigan State University, Brewer took the values of the Munsell color space which describes color as having the attributes of hue (whether it's red, yellow, green, blue, etc.), chroma (the intensity of the color), and value (light or dark) and made detailed charts that gave both Munsell specifications and CMYK (Cyan, Magenta, Yellow, and blacK, the inks that professional printers use) percentages for the colors, with each hue on a separate chart, progressing from light to dark and saturated to dull. These color charts let map makers pick paint chips that have the colors they want on their maps, and then give a printer the CMYK percentages to reproduce the Munsell colors accurately.

With a useful color chart at her fingertips, Brewer decided to see how else she could simplify and standardize map making. One problem she noticed was in the color choices map makers made when showing different percentage values, they often used colors of entirely different hues. "Rainbow colors make data trends hard to see," Brewer says. Instead, she suggests using a single hue but changing its lightness to indicate the change in the percentage value.

Her research has shown that lightness or darkness is perceived as a measure of importance: darker colors signify more, while lighter colors mean less. If the map deals with things of equal value such as which party controls which voting districts the data should be represented with different hues of similar lightness, so as not to imply that one party is better than another. "But if you're talking about percentages or values," says Brewer, "use different color values."

In the map design classes she teaches at Penn State, her students choose their own projects and supply real data to make the maps. The class sometimes proves to be educational in areas outside of cartography, says Brewer. "Last semester, I had a kid who wanted to show that motorcycles were safer than cars," she recalls, pulling his project from a stack of maps in her office. She laughs to see me start, in my face something of the surprise and horror her student must have had when he first made the map, for it displayed quite clearly and graphically how incorrect his assumptions were.

One thing Brewer insists on is using real data in her map-design studies many map researchers simply plug in faked data in areas that seem appropriate, lending, she feels, an artificiality to the research. Brewer has always been concerned with realism and practicality, in both her research and her teaching: "I guess you could say my work has a real applied bent to it."

She pulls open one of the wide, flat map drawers that line one wall of her office: the inside is sprayed with small, colorful maps. "In the past, I've had my students make their final projects into postcards," she says, flipping one over to show the picture caption and tiny stamp square on its white back side. Also in the drawer are maps printed on sandwiched acetate sheets. Brewer peels one sheet back: it is printed entirely in yellow ink. The other sheets are exclusively of cyan, magenta, and black, but when all four are stacked together they make a full-color map. "I really want my students to leave with a piece of publication-ready design work," she explains.

Brewer and her students do their mapping on Macintosh computers, making it easy to change colors and create professional-quality maps. She pulls one up onto the computer screen to demonstrate her research methods. "One thing I'm interested in is how the surrounding colors affect the color you're looking at," she says, adding that her Ph.D. work at Michigan State was in this area. Brewer points to a pale blue section of the map and asks me to match it with the other blues on the map. The task isn't as easy as it sounds, because surrounding dark browns tend to make the blues appear lighter while surrounding yellows make them seem darker and bluer. After some quick double-guessing based on my own painting experience, I choose the correct color from a set of blues on the map. Brewer then switches maps, points to a yellow-green blob, and asks me to match it. "Match it?" I ask. "You mean there's more than one green?" She laughs as she clicks the pointer on the shape, dragging it on top of a similar green the overlapping makes the color difference immediately obvious.

The colorblind, of course, have even greater difficulties with color-recognition. Brewer has been playing with different color schemes to field-test colorblindness studies other researchers have done. For example, while a colorblind individual may confuse red and green, they can differentiate between pink and yellow-green. By making slight adjustments, Brewer can make map colors more distinct.

"But we also have to consider whether nameability of the colors matters," she says. While the readers might tell the colors apart, map communication may still be unclear if they can't properly label them for example, Brewer's description of the "pink" color above was much more convoluted at first: "that reddish, pinkish, purple kind of color."

In addition to color perception, Brewer asks her test subjects specific questions about the maps, to determine how they interpret the data. She asks about basic matches (what percentage is shown in a specific area, for example), whether the levels are higher in one area than another, and if the data is clustered into regions.

"Epidemiologists are very interested in that," Brewer says of the clustering they study clustering, and other patterns of disease spread. Her current project, with Alan MacEachren of Penn State, is to advise the assembly of an atlas showing mortality rates throughout the country for the National Center for Health Statistics, one of the Centers for Disease Control (CDC).

Brewer is currently testing a variety of mapping techniques for the CDC project, to determine for certain which ones will be the most clear and effective to the common reader. "We want an atlas that even your colorblind congressman can read," laughs Brewer.

But after the CDC project, Brewer would like to examine how people who are experts with the data read maps, as opposed to how lay persons do. Possible subjects might be epidemiologists, or environmental researchers studying global change: "people who really want to figure something out, and know their data," she says.

For both experts and novices, Brewer's research could make maps more universally understandable. Her standardization of map conventions could serve as a ][ between those who draw maps and those who read them.